A. Field of the Invention
The present invention relates to a semiconductor device including a field stop (FS) layer, such as a diode and an insulated gate bipolar transistor (IGBT), and a method for producing the same.
B. Description of the Related Art
As a power semiconductor device, for example, there is a diode or an IGBT with a breakdown voltage of 400 V, 600 V, 1200 V, 1700 V, 3300 V, or more. The diode or the IGBT is used in a power conversion apparatus such as a converter or an inverter. The power semiconductor device requires good electrical characteristics, such as low loss, high efficiency, and a high breakdown voltage, and low costs.
As a method for producing the power semiconductor device, the following method has been proposed. First, for example, a diffusion region or a MOS structure is formed on the front surface side of a semiconductor substrate. Then, the rear surface is ground to reduce the thickness of the semiconductor substrate. Proton implantation and a heat treatment are performed for the ground surface to form donors using composite defects including the implanted hydrogen atoms and a plurality of neighboring point defects, thereby forming a high-concentration n-type field stop layer. The donor formed by the composite defect including hydrogen is referred to as a hydrogen-induced donor.
Patent Literature 1 discloses a technique for preventing a reduction in electron/hole mobility at an irradiation position due to proton implantation. Patent Literature 2 discloses heat treatment conditions after proton implantation. Patent Literature 3 discloses an IGBT production method which uses laser annealing when a contact layer is formed after proton implantation and annealing. After the proton irradiation, annealing is performed to recover carrier concentration. Patent Literature 4 discloses a method which recovers a defect layer before proton annealing to increase the carrier concentration of protons. Patent Literature 5 discloses a method which introduces oxygen to a silicon substrate in advance, radiates protons to the front surface, performs annealing, grinds the rear surface, implants phosphorus ions into the ground surface, and performs annealing with a YAG laser. In addition, Patent Literature 5 discloses a method which prevents a reduction in the carrier mobility of a proton-implanted region due to the introduction of oxygen. Patent Literature 6 discloses a method which performs annealing with a YAG laser and a CW laser to form a proton field stop layer (proton donor generation layer) after protons are implanted into the rear surface.